The following references are believed to represent the state of the art:
U.S. Published Patent Application 2004/001592 of Akiwumi-Assani, et al.;
U.S. Published Patent Application 2008/235722 of Baugher, et al.;
U.S. Pat. No. 7,096,481 to Forecast, et al.;
U.S. Pat. No. 7,106,749 to Darshan, et al.;
U.S. Pat. No. 7,634,785 to Smith;
PCT Published Patent Application WO 01/35669 of NDS Limited; and
PCT Published Patent Application WO 03/010970 of NDS Limited.